72 

 ELEMENTARY ENTOMOLOGY. 



SECOND PAPER.— THE GENERAL STRUCTURE OF INSECTS. 



• In those papers of this series which treat of the anatomy of Insects in 

 general, we have largely drawn, with the author's permission, from Prof, 

 J. H. Comstock's excellent " Introduction to Entomology."* 



Thanks to the kindness of Prof. A. S. Packard, we have also made nse 

 of his well-known " Guide" t and his valuahle " Entomology for Begin- 

 ners." I 



As stated in the first paper the hody of an Arthropod, and consequently 

 that of an Insect, is made up of a scries of rings or segments, within 

 which are the vital apparatus and muscles. Confining our attention 

 to insects, it is to be noticed that even young larvae § just hatched from the 

 egg show this segmentation of the body. If such a young larva be 

 examined^r the jointed appearance of the exterior will be seen. The skin 

 of this young larva is quite soft, but becomes harder as the larva grows. 

 This hardening is due to the deposition in the outer layer of the skin 

 (called the cuticle) of a horny substance — chitine. The chitine is deposited 

 in the cuticle of the diflerent segments, but there is left a narrow space 

 around the body between each segment, in which there is little or no 

 chitine. These narrow rings of unafi'ected skin divide the segments from 

 each other, and are termed siUures. Remaining soft, the sutures permit a 

 freedom of motion of the hard segments upon each other. 



In larva} the sutures are usually wider than in the corresponding 

 imagos. Very often the sutures themselves become hardened by chitine, so 

 that the line of separation between two segments disappears. Such an 

 obliteration of sutures occurs very frequently in the head and fore-parts of 

 imagos, and less frequently in the hind parts. 



We have spoken of the segments as hard, but the hard part of any one 

 segment is not a continuous ring. On the contrary, the hard part a segment 

 consists of several pieces which are more or less free to move upon each 

 other. These pieces are the sclerites (from the Greek skleros, hard). Some 

 of the soft cuticle remains between the sclerites, and this separating portion 

 also receives the name of suture, and like an inter-segmental suture may 

 also become " obsolete" (/. e. obliterated). 



The skin, originally soft, but now with its cuticle hardened in the 

 segments, the hard part of each segment consisting of several sclerites, 

 forms the hodij-ioall of the Insect. 



The reader of this series already knows that all an insect's growth is 

 completed in its larval state. As a larva grows quite rapidly, and as chitine 



* An Introduction to Entomology by John Heniy Comstock, Professor of 

 Entomology and General Invertebrate Zoology in Cornell University, and formerly 

 United States Entomologist. With many orginal illustrations drawn and engraved by 

 Anna Botsford Comstock. Ithaca, H. Y. Published by the author 1888, pp. iv, 231, 201 

 figures. Price 2.00 dollars. 



t Guide to the atudy of Insects and a treatise on those injurious and beneficial to 

 crops for the use of Colleges, Farm-schools and Agriculturists by Ali)heus S. Packard, 

 W.D., with fifteen plates and 670 woodcuts ; ninth edition. New York, Henry Holt 

 & Co , 1889. 715 pp. (first edition, 18G0, Salem.) 



X Entomology for Beginners. I'or the use of Young Folks, Truit-growers, Farmers 

 and Gardeners, by A. S. lackard. M.D., Ph. D. ; second edition, revised, A'ew York, 

 Henry Holt & Co., 1889, SG7 pp. 272 figs. 



§ It is hardly necessary to remind the reader that an Insect is an Insect, 

 whether it is an uuhatchad egg, a growing larva, an apparently lifeless pupa, or a flying 

 or creeping imngo. Imagos being so much more conspicuous than the preceding 

 stages, have naturally received both common and soientific names first. 



IT The student cannot be too strongly reminded that he should compare these 

 papers with some insect, say a grasshoiiper. 



